Introduction

Measurement of the brightness of astronomical sources is a fundamental part of all astronomy. The first detections of variations in brightness levels led to the beginning of the recognition of the existence of eclipsing binary stars, thanks to the work of Goodricke (1783), as noted in Chapter 1. Since that time, systematic searches for photometrically variable stars have been conducted by visual, photographic, and photoelectric techniques, and many eclipsing, or photometrically variable, binary stars have been discovered in the process, again as discussed in general terms in Chapter 1. It is therefore no accident that the observational technique of photometry has been the mainstay of studies of binary stars in general, at least in part because photometry can be conducted with very modest equipment and relatively small telescopes. Recent developments in CCD technology that have made it possible to record digital images of small areas of the sky with remarkable photometric precision have further enhanced the value of telescopes of modest apertures in conducting front-line research – for example, the recent discoveries of substantial numbers of eclipsing binaries in the nearby galaxy M31 by Kaluzny et al. (1998, 1999) and Stanek et al. (1998, 1999), who used a telescope of 1.3-m aperture. The current prospects for setting up a global network of programmable robotic telescopes to conduct continuous photometric monitoring of variable sources, including binary stars, are very encouraging, and that will herald a new era in our understanding of the properties of binary stars – magnetic-activity cycles, outbursts, changes in accretion structures, for example.

Chapter 1

1.1 Use Kepler's third law and the small-angle formula to obtain a = 0.051 AU and α = 2.5 mas, still below the currently attainable spatial resolution.

1.2 Use Kepler's third law to obtain a = 19.87 AU, or a = 4270.9 R⊙. Thus both stars have space to evolve independently. The present age of Sirius A is t = 3.28 × 108 years. Sirius B must be massive enough to evolve to a white dwarf in that time. Hence mB = 2.86 M⊙ is the minimum mass for the progenitor of Sirius B, and it must have lost 1.92 M⊙ through the redgiant wind-driven mass-loss phase and the planetary-nebula phase. Discuss whether or not these figures are in accordance with our knowledge of mass loss at different evolutionary stages.

1.3 A CV is composed of a white dwarf and a low-mass main-sequence star. The white dwarf is the degenerate core remnant of a star that was once a red giant. Hence the need for enough space in the binary to allow evolution through the red-giant phase undisturbed, requiring Roche lobes greater than about 100 R⊙. Thus the initial orbital period must have been years, rather than a few as hours as for W UMa systems.

1.4 High-mass x-ray binary (HMXB): 0 star's main-sequence lifetime about 2 × 106 years; A star's, about 100 times longer. 0 star evolves to red-supergiant stage, losing mass to companion through RLOF and mass-ratio reversal.

Introduction

The fundamental equations, relationships, and definitions that we considered in Chapter 2 can be applied directly to interpretation of observational data on binary stars from four types of experiments. The first is spectroscopy, which yields measurements of line-of-sight (or radial) velocities, followed by derivation of the elements of the orbits from those observed velocities. These data furnish the quantities related to the absolute sizes of the orbits and to the masses of the stars in binary systems. The second is pulse timing: measurements of the times of arrival of short pulses of radiation from x-ray and radio pulsars that are found to be members of binary systems, followed by derivation of the relevant orbital elements. Nature has been kind enough to provide us with the kinds of binary stars that will permit both of these independent types of observations to be carried out, with the result that quite complete descriptions of the systems are possible, and observational astronomy can yield directly determined masses for the intriguing end states of stellar evolution: neutron stars and black holes. The third experiment is astrometry: accurate determination of the positions of the components of resolved binaries, both relative to each other and relative to a fundamental astrometric reference frame over the whole sky. Once again, we find some binary systems for which both astrometric data and radial-velocity data are available, so that complete descriptions can be established.

I love being on mountaintops. It's the next best thing to being in space. I guess I also love counting things, whether the things are 4,000 footers in New England, cards in games of chance, or galaxies on my observing list. Therein, of course, lies the tale.

It all started because I was a little kid much more interested in reading than in sports. I grew up in a moderately rough, poor neighborhood in northern New Jersey just outside New York City. I was lucky that both my parents were quite intelligent and always stressed the value of hard work and knowledge. That got me into reading, and science and science fiction were at the top of my list.

The concept of Fate makes me nervous. Yet, with a handful of observations made from our tiny corner of the Galaxy, we can determine the fate of the entire Universe. We have known since the late 1920s that the Universe is expanding. But what we are just beginning to discover is whether the Universe will expand forever or will eventually stop expanding and collapse in on itself.

Modern human civilization now stretches back almost 300 generations to the earliest organized cities. For most of that time, each clutch of humans identified their settlement and its surrounds as their home. Less than 100 generations ago, information transmission and transportation technologies were capable enough for people to form nationstates consisting of many cities and villages and consider them as a new kind of “home.” In the last two generations—with the advent of space travel—many people have come to see their “home” as the whole of the Earth. This is an idea that would have been unthinkable to the ancients—for the world was too large for their technology to integrate the world, or even a nation-state, into an accessible and cohesive community.

So too, though it may not be hard in the future, it is hard for us, now, to think of our “home” as being something larger than our planet. After all, we are still trapped, both physically and to a very great degree intellectually, on our wonderful home, this planet, Earth. A century ago, Konstantine Tsiolkovsky, the great Russian space visionary, described the Earth as the cradle of mankind, saying that humankind, like any infant, cannot live in its cradle forever.

Introduction

One of the assumptions in cosmology is that, no matter where you go in the Universe, the stuff you see when you get there is the same stuff that you already knew about. This is known as the Cosmological Principle. This principle asserts that the Universe, at any given epoch in its history, is homogeneous. Thus all observers should measure the same characteristics and same physical laws, independent of their exact location in the Universe. If this were not the case, then the Universe would be an arbitrary place and there would be no guarantee that, for instance, the law of gravity that holds in New Jersey would be the same as that which holds in California.

Much of observational astronomy is about detecting and classifying the stuff that is out there. For the first 50 years of this century, that task was devoted to stars.

When Alan Dressler called me in 1984, massive black holes were not on my agenda. I had known Alan since the mid-seventies when we were postdoctoral fellows, he at the Carnegie Observatories, I at Caltech. Although we hadn't worked together, his thesis, which included great observational work on clusters of galaxies, was very germane to the theoretical work I had done in my thesis, so I thought he chose good problems and did them well.

By now most of even the lay newspaper-reading public has heard of “dark matter.” Where is it? How much of the stuff exists? What is it? And, incidentally, how sure are we of its presence, or could the whole scientific story for its existence collapse?

Ever since an animal looked up to the night sky, wondered at the brilliance of stars and the vast depth of space, and in the act of doing so became a human being, the Universe beyond our immediate locale was always a subject of human curiosity.

What are we in this world, and how do we relate to the immense emptiness around us that we call space? How did the Universe come to existence?

When I was seven, at my first school book fair, I came away with a title, Insight into Astronomy. The “pull” behind the choice came from the quotation by Ralph Waldo Emerson in the preface: “If the stars should appear one night in a thousand years, how would men believe and adore, and preserve for many generations the remembrance …”

Two days after the Cosmic Background Explorer (COBE) satellite was launched, my wife heard me answer a 4:00am phone call with the words “So we've lost the mission?”. COBE had lost a gyro and we didn't know how well we would recover. Needless to say I got up, only an hour after getting home, to see what could be done.

Gamma-ray bursts (GRBs) were discovered with four US military spacecraft: Vela 5A, 5B, 6A, and 6B, launched in the late 1960s to monitor Soviet compliance with the nuclear test ban treaty. While first bursts were recorded in July of 1969, it took several years to develop proper software to uncover them from a huge volume of data, and the discovery paper by Ray W. Klebesadel, Ian B. Strong and Roy A. Olson of the Los Alamos Scientific Laboratory was published in The Astrophysical Journal on June 1, 1973. This became instant headline news for the astronomical community.